1. Field of the Invention
The present invention relates to a light source device which illuminates a display element and a display apparatus in which the light source device is used and, more particularly, to a light source device used in a display apparatus which is mounted on the head of an observer and displays an image before the observer's eyes.
2. Description of the Related Art
In recent years, a head mounted video display apparatus has been developed which is mounted on the observer's head, enlarges an image displayed on a video display element such as a liquid crystal element, and displays the image in before the observer's eyes, so the observer can observe a large-screen image.
In a video display apparatus disclosed in Japanese Patent Laid-Open No. 11-174988, as shown in FIG. 7, a pair of right and left LCDs 3 serving as two-dimensional video display elements which display images respectively corresponding to the right and left eyes of the observer are arranged inside an outer frame 2 of an apparatus main body 1. A pair of backlights 4 which illuminate the LCDs 3 are arranged behind the respective LCDs 3. A pair of prisms 5 which enlarge the images from the LCDs 3 and guide the enlarged images to two eyes E are arranged under the LCDs 3. The images displayed on the LCDs 3 are guided before the two eyes E of an observer M through observation optical axes L of the prisms 5, enlarged while they pass through the two prisms 5, and projected as if they existed before the two eyes E.
The video display apparatus shown in FIG. 7 employs transmission type video display elements. Images displayed on the LCDs 3 serving as the video display elements are presented to the observer as illumination beams are transmitted through the video display elements.
Each of such transmission type video display elements usually uses a white cold cathode tube as an illumination light source. Usually, R, G, and B color filters are used to generate a color image. Employment of color filters, however, decreases the resolution of a displayed image to ⅓ that of the liquid crystal element itself.
To solve this problem, in recent years, a sequential scheme video display apparatus has been provided. The sequential type video display apparatus does not use color filters but illumination light sources which can emit R, G, and B light. The apparatus sequentially switches the emission colors and the images of the video display elements in accordance with the light emission timings of the respective colors, thereby displaying images.
According to the sequential scheme, the respective illumination light sources of the R, G, and B colors are turned on at a frequency of 180 Hz, which is three times the usual image display frequency of 60 Hz. The video display elements display images in accordance with the light-on timings of the respective colors. This arrangement allows the observer to observe a high-resolution full-color image.
As the illumination light sources employed for sequential scheme illumination, color LEDs having high color reproducibility and high response speed are often used.
According to an example of the arrangement of an illumination device using LEDs, as disclosed in Japanese Patent Laid-Open Nos. 2002-72901 and 2005-249942 (corresponding US Publication No. 2005/0195341A1), dot-like light sources (e.g., LED light-emitting elements) are arranged on a substrate two-dimensionally, and an optical sheet such as a diffusion plate is arranged on a surface that opposes the LED light-emitting elements. This suppresses nonuniform luminance.
A reflection member is arranged on a surface where the LED light-emitting elements are mounted. The reflection member reflects illumination beams to increase the beam utilization efficiency.
In the arrangement disclosed in Japanese Patent Laid-Open No. 2002-72901, the diameter of each opening of the reflection member is larger than that of each dot-like light source. Accordingly, some beams may undesirably leak to the lower side, or the member that forms the dot-like light sources may undesirably absorb the reflected light. Hence, in this arrangement, the reflected light is not utilized effectively.
In the arrangement disclosed in Japanese Patent Laid-Open No. 2005-249942, as the reflection member is arranged under the LED array, the LED array undesirably absorbs the reflected light in a similar fashion. Hence, in this arrangement, the reflected light is not utilized effectively.